Roof decking, also called sheathing, is the structural base of your roof. It’s the layer between the rafters or trusses (the roof’s “bones”) and the shingles or other roofing materials that you see from the outside.
Roof decking is essential for structural integrity and weather protection. It carries the weight of the roofing, snow, and even strong winds. It also contributes to a watertight seal, keeping your home dry and protected from the elements.
In this article, we’ll cover the different types of roof decking available, how it’s installed, how to inspect it for problems, and some common issues to watch out for.
Types of roof decking materials
Roof decking comes in several different materials. Here are some of the most common.
Plywood
Plywood is made of thin layers of wood veneer that are glued together to form sheets. Plywood comes in different thicknesses and dimensions, with different grades for different jobs. For roof decking, you’ll want to use a grade that’s rated for structural use.
Plywood is a popular choice for roof decking because it’s relatively inexpensive, easy to find, and fairly easy to install. It also has a good strength-to-weight ratio, so it can support a decent amount of weight without being too heavy itself.
However, plywood is susceptible to moisture damage and may come apart if exposed to water. Depending on its thickness, it may also need more support than other materials.
OSB (Oriented Strand Board)
OSB is an engineered wood product made from strands of wood that are compressed and glued together. Like plywood, OSB comes in different thicknesses and dimensions, with different grades for different applications.
OSB is often used for roof decking because it’s more resistant to moisture than plywood and has a uniform density. It’s also often less expensive than plywood.
On the downside, OSB can swell if exposed to prolonged moisture, and it may not be as strong as plywood in some situations. Its density can also make it more difficult to work with.
Other materials
Other, less commonly used materials for roof decking include:
- Cement fiberboard: This is a durable, fire-resistant option, but it’s heavier and more expensive.
- Corrugated metal: This is typically used in commercial or industrial buildings because it’s durable and long-lasting.
- Wood boards: This is a traditional option, but it’s less common now due to its cost and availability.
Roof Decking Installation
Installing roof decking is a project best left to the pros, but if you’re a confident DIYer, here are the basic steps.
Preparation
- Inspect the rafters or trusses. Make sure they’re spaced correctly, level, and in good condition. If any of the framing is damaged or weak, repair or replace it before you put the decking on.
- Measure and cut carefully. Measure and cut the decking panels to fit the roof structure exactly. Staggering the seams between panels can add strength.
- Take safety precautions. Wear safety gear, like a harness, hard hat, and safety glasses. Always work in dry weather to avoid slips and falls.
Fastening
- Nailing vs. screwing. Nailing is faster, but screws create a stronger, more secure connection.
- Fastener spacing. Space your nails or screws properly to make sure the decking is attached well. Follow the manufacturer’s instructions and any local building codes.
- Avoid overdriving. Don’t hammer the nails in too far, or you could damage the decking material. Use the right size and type of fastener for your decking material and framing.
Seam treatment
- Sealing. In areas where it rains or snows a lot, you might want to seal the seams with flashing tape for extra weather protection.
- Spacing. Leave a little space between the panels to allow for expansion and contraction. This will keep the decking from buckling or warping.
Inspecting roof decking
You can often spot problems with your roof decking just by looking for a few telltale signs.
Identifying potential problems
- Water damage. Look for water stains, mold, or rot, especially near chimneys, vents, and skylights.
- Sagging. Sagging or unevenness in the decking can mean there’s a structural issue with the decking or framing.
- Delamination or swelling. Plywood can delaminate and oriented strand board (OSB) can swell when they’re exposed to moisture.
- Fastener issues. Loose, missing, or corroded fasteners should be tightened or replaced.
When to call a professional
Some roof issues are best left to the pros.
- If the damage is extensive or significant, it’s time to call a roofing professional. They’ll be able to assess the damage and suggest the best way to fix it.
- If you’re worried about the roof’s structural integrity, get a structural engineer to take a look.
- If you’re not comfortable getting up on the roof yourself, don’t risk an injury. Hire a professional to inspect or repair it.
Common roof decking problems and solutions
Roof decking can develop problems over time, especially if it’s exposed to the elements. Here are some of the most common issues and how to deal with them.
Water damage and rot
Water damage and rot can be caused by leaks, condensation, or poor ventilation. The first step is to find and fix the source of the moisture.
Then, you’ll need to repair or replace any sections of the decking that have been damaged. Improving your roof’s ventilation may help you avoid moisture problems in the future. You might also consider using decking materials that are resistant to moisture damage.
Sagging decking
Sagging decking can be caused by overloading, using decking that’s too thin, or damaged framing. You’ll need to determine why the decking is sagging before you can fix it.
Solutions include reinforcing the framing, adding extra support, or replacing the decking altogether. It’s a good idea to consult with a structural engineer to determine the best way to proceed.
Improper installation
Improper installation can be caused by incorrect spacing of fasteners, cutting the decking improperly, or failing to prepare the roof properly. Be sure to follow the manufacturer’s instructions and local building codes when you install roof decking.
You’ll need to correct any installation errors. That might mean adding more fasteners or replacing panels that were cut wrong. Make sure you’ve prepped the roof correctly before installing new decking.
The Bottom Line
Roof decking is a critical part of your roof, providing structural support and protecting your home from the weather. Without sound decking, even the best shingles won’t do their job.
As we’ve discussed, you have several choices when it comes to decking material. Each material has its pros and cons, and you’ll need to weigh factors like cost, durability, and how well it resists moisture when making your decision.
Whatever material you choose, proper installation and regular inspections are key to making sure your roof decking lasts as long as possible. If you have any concerns about your roof, call a qualified roofing professional right away.